The invention relates to a vacuum cleaner with a dirt collection tank which has a suction inlet and is in flow connection with at least one suction unit via at least one filter and at least one extraction line, and with at least one external air inlet which opens into the extraction line downstream of the at least one filter and can be closed by means of at least one closing valve, wherein the at least one closing valve has a valve member which can be moved back and forth between a closing position, in which it abuts on a valve seat, and an open position, in which it is spaced from the valve seat, wherein it is acted upon by a spring-elastic restoring device with a closing force and in the closing position, in addition, by a magnetic holding device with a magnetic holding force.
Dirt and, preferably, also liquid can be sucked up by means of such vacuum cleaners in that the dirt collection tank is acted upon with a vacuum with the aid of at least one suction unit so that a suction flow is formed and dirt and liquid can be sucked into the dirt collection tank. The vacuum cleaners have one or more filters which are arranged in the flow path between the dirt collection tank and the at least one suction unit and serve to separate solids from the suction flow. During suction operation, dirt particles are increasingly deposited on the side of the at least one filter facing the dirt collection tank and so the filter or filters need to be cleaned after a certain length of time. For the purpose of cleaning, the side of the filter facing away from the dirt collection tank can be acted upon with external air in that at least one closing valve is opened so that external air can flow into the at least one extraction line from the external air inlet and act upon the side of the at least one filter facing away from the dirt collection tank.
A vacuum cleaner of the type specified at the outset is described in the German Utility Model DE 298 411 U1, wherein it is suggested that a suction hose, which is connected to the suction inlet of the dirt collection tank, be closed for a short time for the purpose of cleaning a filter so that a strong vacuum is formed in the dirt collection tank on account of the action of the suction unit. Subsequently, a closing valve is intended to be opened for a short time. The filter then has external air flowing through it in a counterflow direction, i.e., contrary to the direction of the suction flow prevailing during normal suction operation and so dirt particles adhering to the filter become detached.
The use of two filters, which are cleaned alternatingly, is suggested in DE 199 49 095 A1, wherein, during the cleaning of one filter, suction operation can be maintained via the other filter to a limited extent.
The object of the present invention is to develop a generic vacuum cleaner further in such a manner that it makes a particularly effective cleaning of the at least one filter possible.